1. Field of the Invention
The present invention relates to a stacked material which exhibits a photonic band gap characteristic or a filtering characteristic and a light emitting characteristic, and an optical function device using the stacked material.
2. Description of the Related Art
The photonic band gap is a function for limiting the transmittance of light at a particular wavelength by periodically stacking two kinds of materials (A), (B) having different refractive indexes over two or more periods. For example, as illustrated in FIG. 1, the photonic band gap can be realized by periodically stacking a starting stacked structure composed of two layers (A), (B) having different refractive indexes over two or more periods on a substrate (C).
The filtering characteristic, on the other hand, is realized by inserting a layer region (D) having a different thickness from that of the layer (A) or the layer (B) into a portion of the stacked structure of the photonic band gap, for example, as illustrated in FIG. 3. This layer (D) is referred to as a xe2x80x9cdefective layer.xe2x80x9d
Since the energy width of the photonic band gap is proportional to a difference between refractive indexes of the layer (A) and the layer (B), it is important to stack materials which present a large difference between refractive indexes thereof, such as a semiconductor material (for example, a silicon layer or the like) and an insulating material (for example, a silicon oxide film, a silicon nitride film, an air layer or the like).
In general, a vapor phase growth method is used in many cases as a method of fabricating a stacked structure. The vapor phase growth method is most suitable also for growing a layer having a structure conforming to the crystal structure of the substrate (C). However, a stacked structure exhibiting the photonic band gap characteristic is composed of two layers having different crystal structures such as a semiconductor material and an insulating material or crystal and amorphous, so that it has been difficult to fabricate such a stacked structure by the vapor phase growth method while maintaining the planarity of the interface and the integrity of crystal structures.
As a specific example, the growth of a photonic band gap structure with a periodic stacked structure composed of two layers consisting of amorphous silicon and a silicon oxide film (amorphous) has been reported. The amorphous material, however, is not used in semiconductor devices except for solar cells. Therefore, this method may cause a problem when crystal silicon is required.
There is also a report on a photonic band gap structure which is composed of two compound semiconductor layers stacked over four periods. The compound semiconductor layers are each prepared by etching a surface of an epitaxially grown layer in a striped pattern to form periodically striping trapezoids. The two layers are rotated by 90 degrees with respect to each other and bonded. This structure yields a difference between refractive indexes of the atmosphere and the semiconductor stacked structure. However, since a heat treatment is used for bonding, the quality of crystal may be problematic. While several other examples have also been reported, all of them still leave unsolved problems of the quality of stacked crystal, the uniformity of periodic structure and so on.
The present invention has been made in view of the problems inherent to the prior art stacked material, and its object is to provide a stacked material which is formed with a precise periodicity and fabricated without relying on the vapor phase growth method, and an optical function device using the stacking material.
To solve the problems mentioned above, a stacked material in accordance with the present invention is characterized by comprising a multi-periodic stacked structure fabricated by periodically stacking a starting stacked material composed of two alternate layers (A), (B) having different refractive indexes over two or more periods by a substrate bonding method. The stacked material of this structure has a photonic band gap characteristic in the thickness direction. The multi-periodic stacked structure is stacked on a substrate (C).
By including a non-periodic structure in the multi-periodic stacked structure, a stacked material having a filtering characteristic in the thickness direction can be provided.
The use of a smart cut method as the substrate bonding method is advantageous in that the stacked material can be more efficiently and more accurately fabricated.
By providing at least one layer of the multi-periodic stacked structure with a periodicity of different refractive indexes, for example, with a sequence of holes formed therethrough, a stacked material having a three-dimensional photonic band gap characteristic can be provided.
By partly including a non-periodic portion in the periodicity, for example, partly forming holes of the hole sequence at irregular intervals in the foregoing example, a stacking material having a three-dimensional filtering characteristic can be provided.
It is preferable to employ a structure in which the layer (A) is a silicon oxide film, the layer (B) is a silicon layer, and the substrate (C) is a silicon substrate.
It is also possible to employ a structure in which the layer (A) is a silicon layer, the layer (B) is a silicon oxide film, and the substrate (C) is a quartz substrate.
A silicon nitride film may be formed instead of the silicon oxide film.
A compound semiconductor layer may be formed instead of the silicon layer.
An optical function device can be fabricated using any of the stacked materials having a three-dimensional photonic band gap characteristic or a filtering characteristic as mentioned above. The optical function device may be a waveguide, an optical communication modulator, a photodetector and so on.
By providing the non-periodic structure portion with a light emitting ability, for example, forming a region doped with a rare metal such as erbium (Er) or the like between a p-region and an n-region in a silicon layer, light emission is provided. It is therefore possible to provide an optical function device which extracts the light thus emitted as a laser.
A method of bonding substrates applied to the present invention can fabricate any stacked structure composed of not only a semiconductor layer and a semiconductor layer but also all substrates (for example, synthetic quartz and silicon or the like), as long as they have a good surface planarity.